[RFC PATCH 0/5] Support DEVICE_GENERIC memory in migrate_vma_*

[Christoph Hellwig]

On Fri, May 28, 2021 at 11:56:36AM -0400, Felix Kuehling wrote:
> Am 2021-05-28 um 9:08 a.m. schrieb Jason Gunthorpe:
> > On Thu, May 27, 2021 at 07:08:04PM -0400, Felix Kuehling wrote:
> >> Now we're trying to migrate data to and from that memory using the
> >> migrate_vma_* helpers so we can support page-based migration in our
> >> unified memory allocations, while also supporting CPU access to those
> >> pages.
> > So you have completely coherent and indistinguishable GPU and CPU
> > memory and the need of migration is basicaly alot like NUMA policy
> > choice - get better access locality?
> 
> Yes. For a typical GPU compute application it means the GPU gets the
> best bandwidth/latency, and the CPU can coherently access the results
> without page faults and migrations. That's especially valuable for
> applications with persistent compute kernels that want to exploit
> concurrency between CPU and GPU.

So why not expose the GPU memory as a CPUless memory node?